The purpose of this project is to analyze the HBV genome using computer and molecular techniques. Our computer analysis reveals several important findings: (1) We made a detailed study of the organization of the HBV genome and find that it is extremely compact because the virus encodes proteins from overlapping translation frames and because all cis-acting control elements are located within protein encoding sequences. (2) We find that the avian hepadnaviruses possess sequences within the central domain of the core gene that are similar to mammalian hepadnavirus X gene sequences. (3) HBV and retroviruses share features of genome organization and replication. This is significant because it suggests that these diverse virus families evolved from a common ancestral virus.